In recent years, there have been provided copiers capable of successively varying a copy magnification. The applicant of the present invention also suggested and filed such copier on July 13, 1984, with a Ser. No. 630,729, which magnification input means is linked with a numeral calculator function. In operation, according to a divisor function as an example of this numeral calculator function, a length of copy paper and a length of document are respectively input by means of ten keys and the former is divided by the latter to provide a disired magnification. This feature is particularly convenient in case the copy paper and/or the document are not of the standard size. However, according to the contents disclosed in the above application, a copying becomes possible with activation of magnification setting mechanism such as lens movement only after writing a calculated result into a memory by operating a predetermined key after the calculation. It is to be noted here that the memory comprises a non-volatile memory capable, by the operation of the predetermined key, of always reading out the calculated result as a desired magnification. Therefore, if the magnification obtained by the calculation is to be used repeatedly, the above construction is convenient.
However, in many cases, the magnification, which has to be obtained by a calculation, is used only temporarily, and it is inefficient and troublesome to write the calculated result into a memory by operating the key each time a different magnification is to be set.